It is known from U.S. Pat. No. 4,708,203 of Phillips Petroleum, to provide a drill collar to protect equipment during oil or gas drilling operations, the collar being made from fibre reinforced plastics, being generally tubular and having a radially varying cross-sectional thickness.
It is known from GB 1530864 of Reed Tool to provide the exterior of a well tool with a deposit of sintered tungsten carbide in an alloy steel matrix, the deposit being at least partly covered by a layer of cast tungsten carbide welded to the deposit.
U.S. Pat. No. 3,480,094 of Morris suggests a drill collar comprising an elastomeric sleeve, the exterior surface of which includes a plurality of closely spaced ceramic elements to improve its heat and abrasion resistance.
U.S. Pat. No. 3,948,575 of Rosser suggests a drill string comprising annular rings of synthetic resin moulded around the string for non-damaging contact with the well casing.
U.S. Pat No. 4,796,670 of Exxon discloses a drill pipe protector which surrounds and embraces a section of drill pipe. The protector may be of elastomeric material in which a quantity of small hard particles are interspersed.
GB 1542401 of Van Moppes discloses a drill string stabiliser provided with inserts of hard material.
It is also known to coat drill sensors of the kind which provide measurement while drilling with a sheath of wear resisting fibre reinforced epoxy resin insulation.
It is also known to shrink on metal sleeves which are either intrinsically wear resisting or include wear resisting elements. These require that both the drill string outer surface and the sleeve inner surface are precisely machined and circular.
One known wear-resisting treatment uses a welded-on hard metal facing applied directly to the drill string component. Such welding processes adversely affect the parent metal, and lead to degradation of the parent metal. It is an object of the invention to provide a wear protection process which is non-destructive and can thus be repeated indefinitely.
Ideally, downhole drill components should remain integral in use. However it is inevitable that the generally metal components will wear, and I propose a solution whereby when wear occurs, damage is repairable, i.e. the component can be made good without the repair method causing degradation of the drill component. I also propose a solution in which the structure of the drill component is protected from wear.
Any drill debris, i.e. parts which detach in use due to wear, should be drillable. This means that any pieces which break off the drill string should either be soft, e.g. as soft as aluminium, or, if harder than say, cast iron, no bigger in any size than about 0.5 cm.sup.3, the exact volume limit depending on drill bit type, the structure being drilled through, and the drilling conditions.